[PATCH RFC 06/77] PCI/MSI: Factor out pci_get_msi_cap() interface

Alexander Gordeev
2013-10-02T10:48:22Z

This update is needed to facilitate a forthcoming re-design
MSI/MSI-X interrupts enabling pattern.

Device drivers will use this interface to obtain maximum number
of MSI interrupts the device supports and use that value in the
following call to pci_enable_msi_block() interface.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
---
Documentation/PCI/MSI-HOWTO.txt | 15 +++++++++++++++
drivers/pci/msi.c | 33 +++++++++++++++++++++------------
include/linux/pci.h | 6 ++++++
3 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index 35b2d64..1f37ce2 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -169,6 +169,21 @@ on any interrupt for which it previously called request_irq().
Failure to do so results in a BUG_ON(), leaving the device with
MSI enabled and thus leaking its vector.

+4.2.5 pci_get_msi_cap
+
+int pci_get_msi_cap(struct pci_dev *dev)
+
+This function could be used to retrieve the number of MSI vectors the
+device requested (via the Multiple Message Capable register). The MSI
+specification only allows the returned value to be a power of two,
+up to a maximum of 2^5 (32).
+
+If this function returns a negative number, it indicates the device is
+not capable of sending MSIs.
+
+If this function returns a positive number, it indicates the maximum
+number of MSI interrupt vectors that could be allocated.
+
4.3 Using MSI-X

The MSI-X capability is much more flexible than the MSI capability.
diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 875c353..ca59bfc 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -812,6 +812,21 @@ static int pci_msi_check_device(struct pci_dev *dev, int nvec, int type)
return 0;
}

+int pci_get_msi_cap(struct pci_dev *dev)
+{
+ int ret;
+ u16 msgctl;
+
+ if (!dev->msi_cap)
+ return -EINVAL;
+
+ pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
+ ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+
+ return ret;
+}
+EXPORT_SYMBOL(pci_get_msi_cap);
+
/**
* pci_enable_msi_block - configure device's MSI capability structure
* @dev: device to configure
@@ -828,13 +843,10 @@ static int pci_msi_check_device(struct pci_dev *dev, int nvec, int type)
int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
{
int status, maxvec;
- u16 msgctl;

- if (!dev->msi_cap)
- return -EINVAL;
-
- pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
- maxvec = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+ maxvec = pci_get_msi_cap(dev);
+ if (maxvec < 0)
+ return maxvec;
if (nvec > maxvec)
return maxvec;

@@ -859,13 +871,10 @@ EXPORT_SYMBOL(pci_enable_msi_block);
int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec)
{
int ret, nvec;
- u16 msgctl;

- if (!dev->msi_cap)
- return -EINVAL;
-
- pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &msgctl);
- ret = 1 << ((msgctl & PCI_MSI_FLAGS_QMASK) >> 1);
+ ret = pci_get_msi_cap(dev);
+ if (ret < 0)
+ return ret;

if (maxvec)
*maxvec = ret;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index da172f9..2fa92ef 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1144,6 +1144,11 @@ struct msix_entry {

#ifndef CONFIG_PCI_MSI
+static inline int pci_get_msi_cap(struct pci_dev *dev)
+{
+ return -1;
+}
+
static inline int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec)
{
return -1;
@@ -1185,6 +1190,7 @@ static inline int pci_msi_enabled(void)
return 0;
}
#else
+int pci_get_msi_cap(struct pci_dev *dev);
int pci_enable_msi_block(struct pci_dev *dev, unsigned int nvec);
int pci_enable_msi_block_auto(struct pci_dev *dev, unsigned int *maxvec);
void pci_msi_shutdown(struct pci_dev *dev);
--
1.7.7.6